From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757527Ab0DOIsv (ORCPT ); Thu, 15 Apr 2010 04:48:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757449Ab0DOIss (ORCPT ); Thu, 15 Apr 2010 04:48:48 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <4BC5D19A.8000605@redhat.com> References: <4BC5D19A.8000605@redhat.com> <20100406133026.GD20577@parisc-linux.org> <20100326144241.8583.95617.stgit@warthog.procyon.org.uk> <28287.1269625325@redhat.com> <20100326175827.GD20055@linux-mips.org> <17213.1271245760@redhat.com> To: Avi Kivity Cc: dhowells@redhat.com, Linus Torvalds , Matthew Wilcox , Ralf Baechle , mingo@elte.hu, tglx@linutronix.de, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] X86: Optimise fls(), ffs() and fls64() Date: Thu, 15 Apr 2010 09:48:12 +0100 Message-ID: <3879.1271321292@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Avi Kivity wrote: > Even if Intel processors behave that way, other processors (real and > emulated) use those manuals as a specification. Emulated processors are > unlikely to touch an undefined register, but real processors may. > > (qemu tcg appears not to touch the output) Possibly because the AMD64 spec specifies that the destination will be unchanged if the source was 0. David